Process for the preparation of LiBF4

ABSTRACT

The present invention describes a process for the preparation of LiBF 4  by reacting LiBO 2  with 10 to 48% HF solution in aqueous solution at ambient temperature, concentrating the product and recrystallizing to obtain high purity LiBF 4 .

FIELD OF THE INVENTION

The present invention relates to a process for the preparation of LiBF₄.

BACKGROUND OF THE INVENTION

LiBF₄ has very useful applications in high voltage lithium primary/secondary cells. LiBF₄ is well known as a battery electrolyte. This compound was earlier prepared by procedures, which were cumbersome and the yield was poor. The purity of the sample prepared was poor and needed recrystallization.

U.S. Pat. No. 5,079,109 discloses the use of LiBF₄ as a non-aqueous electrolyte for a lithium battery.

While several methods are known for the preparation of LiBF₄ in the prior art such methods suffer from the following disadvantages:

1. The purity of the product is low

2. The yield of the product is low

3. Ambient temperature reaction for the product yield

4. Side reactions occur

5. Multiplicity of steps are required.

OBJECTS OF THE INVENTION

The main object of this invention is to prepare LiBF₄ by a simple chemical reaction.

Another object of the invention is to obtain LiBF₄ with high yield.

A further object of the invention is to obtain LiBF₄ by an efficient process.

The process of the invention overcomes the disadvantages of the prior art enumerated above.

SUMMARY OF THE INVENTION

Accordingly the present invention relates to a process for the preparation of LiBF₄ reacting LiBO₂ compound with 10 to 48% HF solution in aqueous solution at ambient temperature, concentrating the product and recrystallising to obtain high purity LiBF₄.

In one embodiment of the invention, LiBO₂ is suspended in aqueous media/nonaqueous media and reacted with HF.

In a further embodiment of the invention, a paste of LiBO₂ is added in HF.

In another embodiment of the invention, LiBO₂ is pasted with water and reacted with HF.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention LiBF₄ is prepared by treating suspended particles of LiBO₂/Li₂N₂O₄ in aqueous solution or a paste of LiBO₂ in water with HF. The quantity of LiBO₂ and HF are calculated for the reaction separately. After the cessation of the reaction the product was concentrated and crystallized. The product formed was examined and confirmed by x-ray and the purity of the sample was examined.

A calculated quantity of HF was carefully added to a known weighed quantity of LiBO2 in aqueous solution. The reaction was allowed to proceed. When the reaction ceased, the product was concentrated and recrystallized to get very high purity of the sample. The product was examined for its purity and identified by x-ray. FIG. 1 indicates the x-ray analysis which matches with available literature (Table 1).

TABLE 1 LIBF₄ In- 350985 2θ d value intensity OBS tensity Error 1 18.618 4.762 70 18.797 4.717 36 2 2 26.722 3.333 100 26.903 3.311 87 2 3 27.903 3.195 100 28.176 3.165 100 3 4 34.872 2.571 30 5 37.565 2.392 100 37.845 2.375 55 3 6 37.938 2.370 30 37.845 2.375 55 −1 7 39.623 2.273 30 8 44.541 2.033 100 44.732 2.024 75 2 9 48.093 1.890 10 10 50.326 1.812 30 50.521 1.805 17 2 11 52.875 1.730 30 52.875 1.730 12 0 12 54.557 1.681 30 13 57.960 1.590 30 57.960 1.590 13 0 14 63.693 1.460 10 64.005 1.453 7 3 15 65.153 1.431 20 16 68.965 1.361 10 17 71.991 1.311 10 18 73.968 1.280 20 74.078 1.279 8 1 19 78.227 1.221 20 78.227 1.221 10 0 The synthesis of LiBO₂ is disclosed in our copending application.

EXAMPLE 1 Preparation of LiBO₂

Li₂CO₃ (2.96 gm) and B₂O₃ (2.8 gm) are mixed with heating up to 600° C. to obtain LiBO₂ with yield of more than 98%. The colour of the product was white and it was obtained in single phase. The single electrode potential of LiBO₂ with respect to Li in 1M LiClO₄ in propylene carbonate was 2.99 V.

EXAMPLE 2 Preparation of LiBO₂

Li₂OH (1.68 gm) and B₂O₃ (2.8 gm) are mixed with heating up to 600° C. to obtain LiBO₂ with yield of more than 98%. The colour of the product was white and it was obtained in single phase. The single electrode potential of LiBO₂ with respect to Li in 1M LiClO₄ in propylene carbonate was 2.99 V.

The LiBO₂ obtained by the processes of both examples 1 and 2 was high and no side reactions occur.

EXAMPLE 3 Preparation of LiBF₄

LiBO₂ and HF were mixed in a mole ratio of 1:4 by taking HF in water in a Teflon container, keeping the temperature at −4° C., slowly adding LiBO₂. When the reaction ceases, the mixture is slowly heated upto dryness at about 100° C. to obtain dry LiBF₄ with a yield of about 95%. The colour of the product was white and the product was obtained in single phase. The single electrode potential of LiBO₄ with respect to Li in 1M LiClO₄ in propylene carbonate was 2.99 v.

EXAMPLE 4 Preparation of LiBF₄

LiBO₂ and HF were mixed in a mole ratio of 1:4 by taking HF in alcoholic solvent in a Teflon container, keeping the temperature at −4° C., slowly adding LiBO₂. When the reaction ceases, the mixture is slowly heated upto dryness at about 100° C. to obtain dry LiBF₄ with a yield of about 95%. The colour of the product was white and the product was obtained in single phase. The equivalent conductance of LiBF₄ in 1 molar PC at 30° C. was 34.0 ohm⁻¹ cm² mole⁻¹.

In the present invention the following advantages are claimed for the synthesis of LiBF₄:

1. No side reactions occur

2. A one step procedure is sufficient to prepare this compound

3. Required quantity of the product can be prepared by reacting the calculated quantity of reactants.

4. The product obtained is of high purity

5. The product yield becomes 100% if the temperature is kept at −4° C.

6. Wetting of LiBO₂ prevents evaporation of BF₄ formed during the reaction. 

We claim:
 1. A process for the preparation of LiBF₄ comprising reacting LiBO₂ with 10 to 48% HF solution in aqueous solution at ambient temperature, concentrating and crystallizing the resulting mixture to obtain high purity LiBF₄.
 2. A process as claimed in claim 1 wherein LiBO₂ is suspended in aqueous media or non-aqueous media and reacted with HF.
 3. A process as claimed in claim 1 wherein LiBO₂ is pasted with water and reacted with HF.
 4. A process as claimed in claim 1 wherein a paste of LiBO₂ is added to HF. 